“Plants use
underground communication to learn when neighbours are stressed

Chemical signals exchanged via soil
can help prepare corn seedlings for attack by animals or rivals entering their
territory.

By Josh Gabbatiss

Plants use an underground
communication network to exchange chemical warnings, according to a new study.

Work by a team of biologists at the
Swedish University of Agricultural Sciences has provided new insights into the
complex subterranean life of seemingly immobile corn plants.

The work adds to a body of research
exploring the chemical pathways that plants use to “talk” to each other.

“Our study demonstrated that changes induced
by above ground mechanical contact between plants can affect below ground
interactions, acting as cues in prediction of the future competitors,” said Dr
Velemir Ninkovic, lead author of the study.

Plants are known to communicate via
touch. Trees, for example, tend to stop growing outwards when they make contact
with their neighbours’ branches.

However, the mechanisms by which
plants signal using touch are poorly understood, and Dr Ninkovic and his
colleagues wanted to find out whether the answers could be found underground.

In recent years scientists have
begun to disentangle the complex communication system that links plants
together.

Unlike animals, plants do not have
nervous systems and so cannot communicate using rapid electrical signals.

Instead, their signalling both
within their bodies and with neighbours consists of the relatively slow
exchange of chemical messages.

Some of this communication takes
place via strands of underground fungi that plants use to share food, warning
signals and even toxic chemicals – a phenomenon that some biologists have
informally termed the “wood-wide web”.

In the study by Dr Ninkovic and his
colleagues, they wanted to investigate whether chemicals released directly into
the soil by stressed plants could change the behaviour of their neighbours.

The researchers began by applying a
soft brush to corn seedlings, a touch that could represent any number of nearby
stresses, including new plants encroaching on their territory or a plant-eating
animal nibbling on their leaves.

New seedlings were then transferred
into the same growing material as the recently touched plants to see if their
growth was affected – the theory being that plants touched by the brush would
have left chemical traces in the soil documenting their experience.

The scientists found that the fresh
seedlings responded by growing more leaves and fewer roots than plants that had
grown under normal conditions.

They suggested that the corn
seedlings, upon being exposed to the chemical signals of recently touched
plants in the soil, were responding by preparing themselves for the trouble
ahead posed by new neighbours or becoming something’s dinner.

While they seem largely defenceless
against outside attack, plants actually wield a variety of defensive strategies
when targeted by hungry herbivores. Previous research has demonstrated that
plants respond defensively to the sounds that caterpillars make when munching
on their leaves – flooding them with unappetising mustard oil.

To confirm that their plants were
capable of telling the difference between soil occupied by touched and
untouched plants, the scientists gave some corn seedlings a choice about which
medium they preferred to grow in.

The team suggested their results
should be noted by other scientists when conducting experiments with plants, as
even gently brushing a plant’s leaves has the potential to change how it and
its neighbours behave.”

It is
difficult for now to find a direct application of these discoveries in
agriculture.

However, it
is clear that the call made by the Swedish team to fellow researchers around
the world is very relevant, as it is quite likely that many studies in the past
did not take into account these reactions (still unknown) of the plants, even
with a low traumatic action as a gentle brushing.

But
it shows us that the plant world is endowed with many capacities that we have
always believed to be unique to the animal world.